What's your usual build for Teemo? I've been going with Rain Man's Doran'sX2 > Malady > Bloodrazor > Cleaver/Mallet/GA/Banshee's
Malady, while pretty efficient, isn't the best item to get on Teemo early. It's situational.
I run flat ad reds, health quints / flat health regen, flat armor, flat mr, and 0/21/9 (no points in dodge, 3 in ardor). This gives me the feel of having a Doran's Blade at all times. Then I start with
(1a) Boots + 3 Health Pots. Once you hit Lv4 it becomes really easy to harass (you have your move quick and blind). Lv5 you should be harassing a lot, before they get their ult. If you're smart about your Blind you can squeeze in first blood easily.
You're goal is to buy
(2) Wit's End as soon as possible. If you can buy it on your first back, perfect. Otherwise grab 2 Doran Blades or if against an AP carry, some Null-Magic Mantles. Upgrade to
(1b) Merc Treads when you feel it's necessary. Once you have Wit's End you really don't need much else until mid-late game.
Next work on getting
(3) Bloodrazer (or Malady if they have no tank). Buy the AS part of it first unless you need the armor boost from Madred's. After a finished bloodrazer I go for
(4a) Phage (because that 250 health translates to 500 eHP with all my armor/mr). At this point you don't need to upgrade to Frozen mallet ever unless you need survivability against a non-AP carry. Instead work towards a
(5) Banshee's Veil, grabbing Negatron first then catalyst. Finally, you can upgrade into
(4b) Frozen Mallet and grab one last offensive item / some armor.
Another very important item to buy is
Health Potions. I typically grab 3-4 every time I back. It let's me have an edge over an opponent because of that extra 800 health I have. You don't really need wards. Mid-Late game I like grabbing
Oracles cause it's really hard to kill Teemo if you are purposefully avoiding teamfights. Grabbing oracles hints at the opponent that they should really try to kill you, which means you can play like a jerk and waste their time.
Also, you can set your post color (the color all of your posts appear in) in your UserCP > Options or something like that.